Such line connection devices for fluid lines are sufficiently disclosed in numerous publications. Reference will here be made, merely by way of example, to the publications DE 20 2005 013 691 U1, DE 195 10 193 A1, DE 202 14 847 U1, DE 93 07 361 U1 and to DE 298 07 763 U1, DE 200 17 921 U1 and DE 201 15 436 U1.
In motor vehicle engineering so-called selective catalytic reduction (SCR) catalytic converters are sometimes used. In particular, in the case of diesel engines, an aqueous urea solution (e.g. 32.5% urea) may be used as NOx reduction additive. A known problem here is that owing to its relatively high freezing point (approximately −11° C.), a urea-water solution has a tendency to freeze at such ambient temperatures which, depending on the climate and geographical location, are not at all uncommon. The same also applies to water lines for the windshield washer system, unless an adequate antifreeze additive is used. It is commonly known that in the phase change (change in the physical state from liquid to solid), which occurs when liquids freeze, a volume expansion also generally occurs. In practice, therefore, damage and leaks frequently occur in the area of such piping due to the liquid freezing.
If line connection devices of the type described above are now used in such SCR systems, damage due to detachment of the line may occur in continuous service over many cycles of the liquid freezing.
EP 1 553 270 A1 also addresses the problem that difficulties have to be overcome particularly in the case of SCR systems, because the increase in volume that occurs on freezing can lead to damage to components of the SCR unit. In the case of the exhaust gas after-treatment unit described in this publication, at least one reservoir in the form of an expansion chamber, which is intended, in particular through deformation of an elastic expansion part, to accommodate the expanded volume once the medium reaches a freezing pressure, is provided inside the line system. The elastically deformable expansion part may take the form of a diaphragm, which is intended to ensure sufficient elasticity even when subjected to repeated freezing and thawing of the liquid. Since the expansion chamber inside the system is in each case only located at a specific point, however, freezing with the associated consequences can still occur in the rest of the line area and particularly, also in the area of line connection devices.
According, further improvements may be desirable for a connection device of the aforementioned type, which provides a structurally simple and cost-effective design and improved operating characteristics that is especially suited to use in SCR systems and which at the same time avoids damage due to freezing in the connection area of the respective line.